One of the most common devices found in offices all over the world is the stapler. Staplers have been used for years to fasten a plurality of sheets of media together using a thin, U-shaped piece of wire, which is known as a staple. The base of the U-shaped staple is known as the crown, with the legs of the U forming the staple legs. Sheets of media to be fastened together are placed on top of a clinching anvil having recesses formed in the top side thereof. The recesses function as a forming tool to form clinches on the bottoms of the legs, thereby fastening the plurality of sheets of media together.
A cassette designed to hold a plurality of staples therein is conventionally used to supply the stapler with staples. Staples disposed in the cassette are biased toward an end of the cassette, which is located over the clinching anvil. The cassette supports the plurality of staples on a bottom side of the crowns of the staples, with a single staple extending into a fixed slotted aperture located in the end of the cassette. The slotted aperture is located over the anvil, with the slotted aperture being aligned with the recesses in the clinching anvil. The staple extending into the slotted aperture in the end of the cassette is unsupported on the bottom side of its crown.
A driving member, which is typically a thin driving blade, extends into the slotted aperture from the top of the cassette. The driving member is located above the staple extending into the slotted aperture in the end of the cassette. The driving blade is driven into contact with the top side of the crown of the staple extending into the slotted aperture in the end of the cassette. The driving blade may then drive the staple legs into and through the plurality of sheets of media located adjacent to the clinching anvil. After the staple legs pass through the media, the legs contact the recesses disposed in the top side of the clinching anvil. When the staple legs extend into the recesses in the clinching anvil, they are clinched, typically towards each other, to thereby retain the staple in the plurality of sheets of media to keep the plurality of sheets of media together.
The driving blade is driven by hand in simple desktop staplers, often with a single swift impact from the user's hand. This impact is usually more than sufficient to drive the staple into the sheets of media and to clinch it on the bottom of the media. In a slightly more sophisticated stapler, the impact is provided electromechanically. Sheets of media may be inserted into position against the clinching anvil at which time an electrical trigger may cause operation of the driving blade. In heavy-duty industrial applications, a stapler may even be operated using pneumatic pressure to operate the driving blade.
Many conventional staplers have at least one cassette containing a row of preformed staples of a particular size (i.e. the staples are already bent into a generally U-shaped configuration). Most conventional staplers are designed to drive a staple of one particular leg size only, with that size staple being best applied to use to fasten together a specific range of numbers of sheets of media.
For example, a short leg (one-quarter inch, for example) staple may be used to fasten from two to twenty-five sheets of standard 20# media together. If a greater number of sheets of media are to be fastened together using a short staple, they will not be fastened together securely because the staple legs are too short. Similarly, a long leg (three-quarter inch, for example) staple may be used to fasten from fifty to one hundred and fifty sheets of standard 20# media together. If a smaller number of sheets of media are to be fastened together using a long leg staple, the staple legs will be over-clinched. An over-clinched staple may have legs that extend through the sheets of media in an undesirable manner.